1. Field of the Invention
The present invention relates to methods which make it possible to improve the breeding conditions for piglets (newborn pigs).
2. Description of Related Art
It is known that the productivity of pig farms in France and worldwide remains limited by a high postnatal mortality, this being in spite of the improvements which have been made in the past few years relating to breeding techniques, especially in terms of nutrition and control of the surroundings and of the pathologies affecting the species.
Thus, by way of illustration, the numbers for the amount of losses for 1996 in France are up to about 18% of the total number of newborns, which corresponds to about 5% of stillborn piglets, while 13% of the liveborn piglets die between birth and weaning, of which half during the first 48 hours following birth.
While a number of causes have been put forward to explain this relatively high mortality rate, causes such as the crushing of the newborns by the sow, sensitivity to cold and also certain pathologies, the fact remains that a quarter of this postnatal mortality can, it seems, be attributed to a phenomenon of hypoxia resulting from farrowing and affecting the thermoregulatory function and the vitality of the newborn (see for example the article by P. Herpin et al. which appeared in Journees sur la Recherche Porcine en France in 1997, page 29).
Indeed, during farrowing in sows, which can last for several hours, the repeated uterine contractions can reduce exchanges between the fetus and the placenta, which can cause a drop in blood flow rate across the placenta and sometimes even a premature detachment of the placenta or a rupture of the umbilical cord. It is known that this risk increases with the duration of farrowing, with the size of the litter, but also with the order of birth within this litter.
It is known, moreover, that the lightest piglets are more subject to this hypoxia phenomenon. It should also be noted that even if the piglets are alive after farrowing, they can suffer and retain sequelae from this neonatal hypoxia because a few minutes of anoxia is sufficient to inhibit the respiratory centers and to cause irreversible legions in the brain of the piglets.
The degree of hypoxia in the piglets at birth may be measured in particular by one or more of the following blood factors: PA1 the partial pressure of oxygen or of CO.sub.2 ; PA1 the pH; PA1 the lactate content. PA1 the piglets are placed after birth in a closed or semiclosed chamber; PA1 a gaseous mixture containing oxygen is injected into the chamber; PA1 is characterized in that the oxygen content of the gaseous mixture is between 25 and 50%. PA1 the oxygen content of the gaseous mixture is in the range from 30 to 50%, and still more preferably in the range from 35 to 45%; PA1 the piglets are placed in the chamber within the hour following birth; PA1 the piglets are placed in the chamber within 30 min following birth, and still more preferably within 20 min following birth, or even immediately after birth; PA1 the piglets are kept in the chamber, in the atmosphere consisting of the gaseous mixture, for a period of 5 to 30 min; PA1 the piglets are kept in the chamber, in the atmosphere consisting of the gaseous mixture, for a period of 10 to 25 min; PA1 the gaseous mixture, previously injected into the chamber, was made humid; PA1 said gaseous mixture containing 25 to 50% oxygen is used during the whole or part of the farrowing proper.
A hypoxia is then characterized by a low pH, a high lactatemia and a high partial pressure of CO.sub.2.
It can also be stated that one of the consequences of the phenomenon of hypoxia in piglets, through the fact that it reduces the physical vitality of the animal (stability, attempts to stand up), is to delay the piglets' first contact with the teat and therefore the first sucking which is necessary not only in terms of supply of energy for thermoregulation, but also for acquiring immunoglobulins.
Document FR-A-2,710,816 provides a method and a plant for improving the breeding conditions for animals in a closed or semiclosed chamber, such as using an injection of oxygen at periodic intervals or during selected periods such as the meals, service periods or alternatively periods preceding or following birth, the content of oxygen in the surrounding air then being maintained between 20.5 and 21.5%. The objective sought by this document is to solve a problem of mortality of the individuals, especially in a period of heat, and for example for newborns during premature births or births after term.
The approach followed by this document is to maintain the oxygen level around the atmospheric content and is therefore to adjust this content to around 21%, the oxygen in the surrounding atmosphere indeed having a tendency to decrease substantially in intensive breedings because of respiration by the animals.
The approach of this document is therefore rather attached to a renewal of the surrounding atmosphere which becomes depleted over time.
There may also be mentioned the case of the document FR-A-2,645,403 which provides a method of breeding living beings in an oxygenated medium in order to increase their size, the objective being to make it possible to increase the size of the animals "up to several ten of times" depending on the species and "to cause them to gain more meat".
Besides the fact that the document is based on reasoning which is not very scientific (such as mentioning the size of dragonflies and other crickets in the Jurassic period), it remains silent on the oxygen conditions to be applied in order to achieve such objectives, and a fortiori completely ignores the problems of postnatal mortality.